The present invention relates to a tank block for use in forming the walls of glass-tank furnaces, and of the type having an inner surface which faces the glass bath within the furnace, an opposite outer surface facing away from the bath, a head or upper portion having therein a recess or step facing the outer surface and a base or lower portion.
The present invention further relates to a tank block having a head portion, a base portion and an opening extending through the tank block from the inner surface to the outer surface thereof and employed for the introduction of an electrode.
In glass-tank furnaces, the walls of the tank chamber or basin are lined with large size brick blocks made of high grade and heat resistant ceramic refractory material having a high resistance to corrosion from the glass melt in the furnace, while the joints between the block are as few in number and as small as possible.
The blocks have square or rectangular sides and usually possess dimensions between 1200 .times. 500 .times. 300 mm and 500 .times. 400 .times. 200 mm. Smaller sized blocks are not normally employed as tank blocks due to the relatively increased number of joints that are involved.
The blocks of the tank basin are attacked by the liquid glass melt during the operation of the tank furnace installation.
The degree of corrosion of the tank blocks by the glass melt is a function of the refractory ceramic material of the blocks, the mineralogical and physical properties of the material of the blocks, the temperature of the glass melt, special conditions with respect to the level of the bath and the temperature drop outwardly through the wall. The strongest corrosion of the tank blocks takes place in the areas of the highest temperature and the highest glass flow. In the case of upper flame heated tank basins, strongest corrosion occurs at the level of the upper surface of the bath, i.e. in the upper or head portions of the tank blocks. In the case of electrically heated installations, strongest corrosion occurs at the area around the point where the electrode extends through the wall into the basin.
In order to reduce the corrosion caused by the glass melt at the level of the bath line or in the area of the electrodes, and to thus equalize the wear profile and to increase the service life of the tank blocks, external air cooling may be provided in the areas of strongest corrosion, especially when the corrosion is already in a highly advanced state. This exterior cooling, in connection with tank blocks that have a step or recess facing the outer surface in the head portion of the tank block, i.e. the so-called recessed or cooling blocks, so as to provide a reduced wall thickness at the level of the bath line, leads to an effective cooling effect. The employment of recessed tank blocks makes it possible to retard progressive corrosive wear of the block in the area of the recess as a result of increased air cooling and also through the use and placement of hot repair bricks, so that the corrosive wear line may be more favorably controlled.
It is also known that in the areas of the tank blocks that are subjected to less corrosion the effect of heat insulation can be achieved by means of bricks or plates without negative effect.
Due to the high requirements placed on the tank blocks, the tank blocks are formed as high-density compact elements based on raw materials that contain alumina, silicic acid and zirconium oxide, in accordance with the following processes: fusion casting, casting of a ceramic suspension and ceramic firing, pressing or compacting a ceramic granular mixture and ceramic firing. Such blocks are very expensive and costly to manufacture. Furthermore, in spite of all efforts to obtain a balanced corrosion wear line, the service life of the recessed tank blocks is substantially determined by the particularly strong corrosion in relatively small zones, namely in the area of the bath level line or in the area of the electrodes. Consequently, large portions of the expensive tank block material, in the areas thereof which are subjected to only low corrosion, are not effectively used, and in fact are wasted.